Ultrafast Preparation of Three-Dimensional Dendritic Gold Nanostructures in Aqueous Solution and Their Applications in Catalysis and SERS

Abstract

Three-dimensional dendritic gold nanostructures were prepared via an ultrafast one-step homogeneous solution method. Cationic surfactants, decane-1,10-bis(methylpyrrolidinium bromide) ([mpy-C 10 -mpy]Br 2 ), were used as the capping agent and L-ascorbic acid (AA) was used as the reducing agent. The as-prepared gold dendrites present a [111] plane and grow along the AE211ae direction. The AA plays an important role in the formation of the dendritic nanostructures. The methylpyrrolidinium quaternary ammonium headgroups and bolaform nanostructures of the surfactants are the key factors for the formation of dendritic structures. Further investigation revealed that the reaction time and concentration of HAuCl 4 weakly affect the formation of the dendrites. Moreover, the obtained gold dendrites exhibit excellent activity toward the catalytic reduction of p-nitraniline and higher enhancement of surface-enhanced Raman scattering when using Rhodamine 6G as the model molecules. ' INTRODUCTIONShape controlling of nanostructures became the third major topic coordinated with elemental composition and size control in the chemistry of nanostructures 1 since the morphology of nanostructures considerably influences their intrinsic properties and relevant applications. 2 Noble metal nanostructures, especially gold nanomaterials have attracted tremendous interest due to their fascinating physical and chemical properties and promising application in catalysis, nanoelectronics, sensors, photonics, imaging, and biomedicine. 1À3 Great effort has been devoted to synthesize shape-controlled gold nanostructures. 4 Among a variety of gold architectures, such as rods, 5 wires, 6 belts, 7 cubes, 8 polyhedra, 9 plates, 10 stars 11 and dendrites, 12 which have been widely achieved by certain methods, dendritic surpermolecular nanostructures attracted our attention with their unique morphology and properties. Dendritic nanostructures have special texture nanostructures, such as sharp edges or tips, nanoscale junctions and high surface areas, which brought the potential applications in biosensor, electronics, catalysis, and surface-enhanced Raman scattering (SERS) based analysis. 13 However, Au crystals usually exhibit a highly symmetric facecentered cubic (fcc) structure, and the dominant facets possess similar surface free energies. These features lead to the difficulties in forming dendritic nanostructures with complicated morphologies in homogeneous aqueous solution. The good news is that various methods, such as electrochemical, metal-deposition, and the solution-phase method, have been developed to fabricate dendritic noble metal nanostructures in recent years.The electrochemical method is a traditional way to obtain noble metal dendrites or thorn nanostructures. For example, Pt, Ag, and Au branched or dendritic nanostructures were all obtained by this method. 14 The metal deposition method is another way to obtain dendrite nanostructures. Weak reductive metal zinc plate has been used as deposing metal and reducing agent in the fabrica...

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